System and method for hybrid automatic repeat request timing for device-to-device communication overlaid on a cellular network

ABSTRACT

An embodiment of a system for operating a communications controller for a group of user equipments engaged in a DMC link in a wireless communications system is provided. The communications controller is configured to allocate a set of subframes in one periodic group of subframes to the group of UEs for the DMC link, signal the set of allocated subframes to the group of UEs, and transmit parameters related to a group of HARQ processes of the DMC link. In an embodiment, the communication controller uses HARQ processes for cellular UE transmission that are determined independently from HARQ processes of the group of HARQ processes for the DMC link, and the parameters are configured to enable the group of UEs to manage the group of HARQ processes for the DMC link.

TECHNICAL FIELD

The present invention relates generally to a system and method fordigital communications, and more particularly to a system and method foroperations enabling direct mobile communications in a wirelesscommunication system.

BACKGROUND

In the field of wireless communication, there has been increasing demandfor direct device-to-device communication (“D2D”), direct mobilecommunication (“DMC”), and the like. This form of communications refersto a communications mode between a group (two or more) of userequipments (“UEs”) that does not include or does not always include acommunications controller in a communication path between or among theUEs. DMC is used herein to denote this form of communication. Generally,a DMC link involves direct communications between a group of DMC devicesoccurring as point-to-point (“PTP”) communications, either aspoint-to-single-point, or as point-to-multipoint, without having thecommunications passing through and being fully controlled by acommunications controller, such as an evolved NodeB (“eNB”), a NodeB, abase station, a controller, a communications controller, and the like.DMC devices are commonly referred to as a user equipment (“UE”), amobile station, a mobile, a communications device, a subscriber, aterminal, and the like. A DMC link is different than a cellular link. Acellular link between UEs involves data shared between the UEstransiting through a network infrastructure node such as an eNB, relaynode, or the like. Note however, that for a DMC link, while data isdirectly exchanged between the UEs, control information for the DMC linkcan still transit through a network node. DMC can enable a cellularnetwork to offload a portion of its base station traffic. In addition tooffloading base-station traffic, DMC also enables proximity-basedadvertisement for local business entities, which can be a revenue sourcefor such entities. DMC can also enable an end user of a user equipmentto find and identify nearby friends. Ad hoc-type services can also beprovided among user equipments that are physically near each other. DMCis also a key enabler of local social networking.

Processes to provide performance enhancements for DMC would accelerateadoption of this communication form in the marketplace.

A process for a base station to reduce communication with userequipments desiring to communicate with each other without incurringunnecessary cost and overhead would facilitate offloading traffic from abase station.

SUMMARY OF THE INVENTION

Technical advantages are generally achieved by embodiments that providea system and method for device-to-device operations in a wirelesscommunication system.

In accordance with an example embodiment, a system and a method foroperating a communications controller in a wireless communicationssystem for a group of user equipments engaged in a DMC link areprovided. For example, embodiments provide a system constructed with atransceiver and a processor coupled to the transceiver. The processor inconjunction with the transceiver is configured to allocate a set ofsubframes in one periodic group of subframes to the group of UEs for theDMC link, signal the set of allocated subframes to the group of UEs, andtransmit parameters related to a group of HARQ processes of the DMClink. In an embodiment, the communication controller uses HARQ processesfor cellular UE transmission that are determined independently from HARQprocesses of the group of HARQ processes for the DMC link, and theparameters are configured to enable the group of UEs to manage the groupof HARQ processes for the DMC link.

Further embodiments provide a system and a method for operating a userequipment engaged in a DMC link in a wireless communications system. Forexample, embodiments can provide a system constructed with a transceiverand a processor coupled to the transceiver. The processor in conjunctionwith the transceiver is configured to receive from a communicationscontroller an allocation of a first set of subframes for a group of UEsfor the DMC link, and receive from the communications controllerparameters related to a group of HARQ processes of the DMC link. In anembodiment, the UE manages a group of HARQ processes of a cellular UEtransmission and at least one HARQ process from the group of HARQprocesses of the DMC link, and the UE maps the at least one HARQ processfrom the group of HARQ processes based on the allocated first set ofsubframes and the received parameters.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates a system drawing showing a base station thatcommunicates in a cellular network with UEs that communicate with eachother directly over a DMC link, illustrating an environment forapplication of the principles of an embodiment;

FIG. 2 illustrates a DMC time resource allocation process, in accordancewith to an embodiment;

FIG. 3 illustrates a flowchart showing an embodiment of communicationscontroller operation to inform each UE of a DMC group of particularcommunication time resources for the DMC group;

FIG. 4 illustrates a flowchart of an embodiment of UE operations todetermine whether to transmit or receive;

FIG. 5 illustrates an example of mapping Hybrid Automatic Repeat reQuest(“HARQ”) processes to allocated subframes, in accordance with anembodiment;

FIG. 6 illustrates an embodiment of communications controller operationwith the new HARQ process;

FIG. 7 illustrates a flowchart of an embodiment of UE operations whenthe UE in a DMC group receives signaling including information about themaximum number of HARQ processes;

FIG. 8 illustrates a flowchart of an embodiment of UE operations for aHARQ process on a given subframe;

FIG. 9 illustrates a graphical representation of ACK/NACK feedback withexplicit indication of an acknowledged HARQ process number;

FIG. 10 illustrates an embodiment of a process performed at a UE forsending ACK/NACK along with an indication of the HARQ process number;

FIG. 11 illustrates an embodiment of UE operation to assess if a packetwas correctly received by the other UEs in a DMC group when ACK/NACKsare sent by other UEs in the group;

FIGS. 12 and 13 illustrate graphical representations of ACK/NACKreporting with a sliding window, in accordance with an embodiment; and

FIG. 14 illustrates a block diagram of elements of a processing systemthat can be used to perform one or more of the processes discussedhereinabove.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

It should be appreciated that embodiments provide many applicableconcepts that can be embodied in a wide variety of specific contexts.The specific embodiments discussed below are merely illustrative ofspecific ways to make and use an embodiment, and do not limit the scopeof the invention.

DMC enables a cellular network to offload traffic to a wirelesscommunication path without much involvement of a communicationscontroller, e.g., a base station, in the communication link between UEs.DMC can also enable easy data transfers to and from diverse peripheraldevices such as printers, cameras, personal computers, televisionreceivers, etc., that are colocated in the physical environment of theend user. For example, devices within some radius, such as a distance(e.g., a distance of 50 meters) or by acceptable physical measures(e.g., power levels) of the end user could be considered colocated.Nonetheless, cellular operators generally desire to have DMC under theircontrol for purposes of billing and accounting, management of carrierfrequencies and interference, and overall management of network trafficto optimize available bandwidths.

Although the term “direct mobile communication” generally refers to acommunication mode between user equipments that does not include acommunications controller in a communication path between the UEs, it iscontemplated herein that DMC refers generally to the concept of a groupof communicating devices that need not include communication with acellular base station.

An embodiment enables a communications controller to allow users tocommunicate with each other directly without incurring unnecessary costor signaling overhead.

Referring to FIG. 1, illustrated is a system drawing showing acommunications controller, e.g., an eNB 110, that communicates in acellular link with a group of UEs (UEs 120, 130), and the UEs 120, 130communicate with each other directly over a DMC link, illustrating anenvironment for application of the principles of an embodiment. Thegroup of UEs comprises two or more UEs. The eNB 110 communicates controlinformation with the UEs 120, 130 over uplink/downlink wirelesscommunication links 140, 150. The served area 115 of the eNB 110 isindicated by the dashed line 115. The UEs 120, 130 directly communicatedata with each other over DMC link 160.

A DMC link is a direct communication link between two or more UEswithout much involvement of network functionality, such as provided by acommunications controller, for the communication link between the twoUEs, as shown in FIG. 1. There are two main ways of implementing DMC. Ina device-centric arrangement, a DMC connection is without networkoversight. In a network-centric arrangement, the network initiates theDMC connection between a group of UEs (DMC UEs) when conditions areappropriate and assist the DMC UEs to communicate with each other duringa DMC link, for example, transmitting control information, allocatingresources, etc. Conditions include local parameters such as theproximity of the devices as well as macro parameters, such as overalltraffic demand, location of non-DMC devices, etc. A network-centricarrangement offers potential for offloading local traffic from thenetwork, which is attractive to cellular operators.

With a network-centric approach, the DMC UEs need to be aware of whichtime resources (e.g., subframes) are allocated by a communicationscontroller for the DMC group. Several processes to allocate resourcesare introduced herein for a DMC group. Processes are provided to ensurethat HARQ timing is maintained, and for acknowledgment/negativeacknowledgment (“ACK/NAK” or “ACK/NACK”) feedback.

When DMC link for a DMC group is established, resources for this groupof UEs to communicate on are allocated. Communication resources, both intime and frequency, are allocated to the DMC link. The allocation of theresources for DMC is addressed herein.

DMC can either be a single link with only two devices communicating, asshown in FIG. 1, or it can be multi-link, with multiple devices engagedin DMC. While a main focus is single-link DMC, multi-link DMC is alsodeemed of high interest from a business perspective. For instance, manyusers can set up a local multi-point DMC group as a local socialnetwork, for example, group-chatting within a high school, enabling theability of several people to play games, or exchanging files byparticipants in a meeting. The processes introduced herein are targetedto allocate resources for both multi-link and single-link DMC.Communication resources are allocated efficiently for multiple UEswithout excluding single-link UE pairs with high performance. In thefollowing, a DMC group is taken as an example without losingcommonality.

In order to keep UE complexity low, a half frequency-division-duplex(“FDD”) communication protocol for the DMC link is assumed in the uplinkband. Although FDD protocol is described, time-division-duplex (“TDD”)communication protocol can also be used for DMC. This usage of theuplink band implies that a UE should not simultaneously receive andtransmit on DMC resources. Consequently, if one UE is transmitting onthe DMC link, the other DMC UEs should be prepared to receive. For thepurpose of correctly transmitting and receiving a packet, the UEsinvolved in a DMC group (single-link or multiple-link) are informedwhen, the time resources, where, the frequency resources, and how, therelated HARQ procedure, modulation and coding scheme (“MCS”), power, andmulti-input/multi-output (“MIMO”) scheme to transmit and receive.

To address the “when” aspect, consider for a general solution for asemi-static arrangement that a group of k (k>1) UEs is grouped togetherto establish a DMC group. Any UE within this group can communicatedirectly to other UE(s) within the group. The time resources areallocated to the UEs by higher layer signaling, e.g., radio resourcecontrol (“RRC”) signaling from the communications controller or acontrol channel. Herein, a control channel comprises a physical downlinkcontrol channel (“PDCCH”), an enhanced physical downlink control channel(“ePDCCH”), a physical broadcast channel (“PBCH”), and the like. Inorder to simplify the description, the following assumptions areadopted:

In a first assumption (“P1”), only one UE transmits information at agiven time within a DMC group, and in a second assumption (“P2”), anentire time transmit unit (time domain only), for example, a subframe,is allocated to a single UE.

Transmission or reception of information is understood to comprisetransmission or reception of data and/or control information. A HARQprocess is understood to manage a data transmission.

The first assumption (P1) eliminates the need for frequency multiplexingof DMC UEs. This relaxes constraints on power control, time, andfrequency synchronization. The second assumption (P2) indicates thattime-domain granularity is not necessarily needed, but makes thedescription simpler, i.e., the described processes could be applied witha different temporal granularity, such as a slot or a set of severalsubframes. However, considering practical constraints such as the needfor a DMC UE to alternate between transmission and reception, latencyconstraints, etc., a temporal granularity of one subframe appears to bereasonable.

Turning now to FIG. 2, illustrated is a DMC time resource allocationprocess, in accordance with an embodiment. A DMC group is formed withfour UEs, for example. A set of subframes, any of which can be used forcellular or DMC transmission, are indicated by the reference numeral210. Ten subframes generally form a radio frame, periodically repeat intime. In various applications, the set of subframes can number 20 or 40,or another number, instead of ten. The communications controllerperforms several actions: Four subframes of the set of 10, indicated inFIG. 2 by crosshatching in 210, are allocated for DMC among the group offour UEs. The communications controller allocates a first set ofsubframes, the four subframes, indicated by the group 220 whichperiodically repeats over time with a period that matches the subframes210, for DMC for the four engaged UEs. Collectively, the four UEs as agroup can transmit information on any of the subframes allocated forDMC. Within the group of UEs, the communications controller decideswhich particular UE transmits information on a given subframe, asillustrated for the particular UE, crosshatched, in the group ofsubframes with reference numeral 230. The other UEs or some of the otherUEs receive on that particular subframe. Accordingly, each UE isinformed by the communications controller, using a second set ofsubframes, when to transmit information in the group of subframesallocated for DMC (i.e., the first set of subframes), and each UE candeduce in a complementary manner when to receive information. In anotherembodiment, the allocated subframes for the DMC group can be indicatedto UEs in the group differently. For example, UE 1 can be indicated that3 out of 10 subframes are allocated; UE 2 can be indicated that 4 out of10 subframes are allocated, so UE 1 may not receive all the informationtransmitted by other UEs. In other words, only a subset of the subframesnot allocated for transmission of information can be used for receptionof information, although this complicates the HARQ process and timing.

Turning now to FIG. 3, illustrated is a flowchart illustrating anembodiment of communications controller operation to inform each UE ofthe DMC group of the particular communication time resources for a DMCgroup, i.e., the particular subframe allocation. Based on this process,communications controller operation is as follows. The process begins instep or block 310. In step or block 320, the communications controllerestablishes a DMC group based on, e.g., a user request, observation oftraffic patterns among UEs, etc. In step or block 330, thecommunications controller notifies each UE of its membership into theestablished DMC group. Notification can be sent by higher-layersignaling (e.g., RRC signaling), and could be either an individualmessage to each of the UEs, or a multi-cast message to the entire group.

In step or block 340, the communications controller determines a set Sof subframes allocated to the DMC group that was formed, and determinesin step or block 350 when each UE will transmit information and when itwill receive information within the set of subframes S. In step or block360, the communications controller informs the DMC group (e.g., by RRCsignaling) of the subframe allocation for the particular group (a firstset S), and, in step or block 370, informs each UE of the group of theparticular subframe allocation within the group. The UE can transmitinformation on subframes of its particular subframe allocation (a secondset). This second set is a subset of the first set. For each UE, thesubframes of the first set not in the second set are allocated forreceiving DMC transmissions of information from other UEs in the groupof UEs. There can be several ways of conveying the information to theUEs. For example, steps 330, 360 and 370 can be implemented by acombined message or by a two-step message having 330 and 360 as a firststep message, and 370 as a second step message. The process ends in stepor block 380.

Time resource allocation for an entire DMC group can be an efficientmulti-cast RRC message sent to the entire DMC group. Time resourceallocation for a particular DMC UE within the DMC group can be eitherindividual RRC signaling for each UE or multi-cast RRC signaling to allthe UEs in the DMC group. Note that these two messages can be lumpedinto a single message. This is particularly attractive when there areonly two DMC UEs in the group. Note also that in order to keep signalingas simple and with as low overhead as possible, the time resourceallocation for a particular DMC UE can only indicate the UE to transmitinformation on a given subframe, with the implicit understanding that onany unassigned DMC subframe, the UE is to listen and potentially receiveinformation.

Several alternatives can be employed for allocation of communicationtime resources for a DMC group.

A first alternative is to specify subframe assignment with a bitmapmessage.

This signaling can include two different bitmaps, one to indicate whichsubframes are allocated to the DMC group, and one to indicate whichsubframes are allocated to a particular UE. These two bitmaps can besent in two different messages, or can be combined into a single bitmapsent in a single message.

Over a given period (e.g., 10 ms, 20 ms, or 40 ms), a bitmap message canbe employed to indicate which subframes are collectively assigned to aDMC group, and/or to a particular UE in that group for transmission. ADMC subframe not assigned to the particular DMC UE for transmission isassumed by that particular DMC UE to be used for reception. In analternative embodiment, the bitmap message indicates which subframes arecollectively assigned to a DMC group, and/or to a particular UE in thatgroup for reception. It is recognized that if a message designates aparticular subframe for transmission, with the understanding thatremaining subframes designated for reception, the message can beequivalently inverted to designate a particular subframe for reception,with the understanding that remaining subframes are designated fortransmission. In the interest of brevity, the distinction betweendesignating a particular subframe for transmission or for reception willnot be further described herein.

Bits corresponding to DMC subframes in a bitmap message can be assigned“1” when bits corresponding to non-DMC subframes are assigned, or “0,”and vice versa.

The bits corresponding to a subframe for particular UE for transmissioncan be assigned “1,” while “0” means that the subframe is for reception,or vice versa. Alternatively, if the bitmap is sent to several UEs or toall the UEs in the DMC group, a UE ID could be used to indicate if asubframe is allocated to a particular UE or not.

As an example, if the subframe period is 10 subframes, numbered 0, 1, 2,3, . . . , 9, and two UEs form a DMC group of size two, thecommunications controller can send a binary message “1010000000” to theDMC group, allocating subframes 0 and 2 to the group every 10 subframes.Subframes 0 and 2 represent the first set of subframes. Thecommunications controller can send a second message “10” to the firstUE, allocating the first DMC subframe to the first UE for transmissionon the DMC link. For the first UE, the second set of subframes wouldcontain subframe 0. The first UE also knows that it can transmitinformation on subframe 0. As a result of knowing the first and secondsets, the first UE determines that it can receive information onsubframe 2. The communications controller sends another message“01” tothe second UE, allocating the second DMC subframe to the second UE fortransmission. For the second UE, the second set of subframes wouldcontain subframe 2. Any subframe not allocated to a particular UE fortransmission is presumed in complementary fashion by that UE to be usedfor reception.

The eNB can combine the two messages into a single message, for example,by replacing the first bit “1” in message “1010000000” that allocatessubframe 0 to the DMC group with two bits “10” that allocates the firstsubframe to the first UE to transmit information on a DMC link,replacing the second bit “1” that allocates subframe 2 to the DMC groupwith two bits “01” that allocates the third subframe to the second UE totransmit information on a DMC link, replacing each remaining “0” withtwo bits “00”, etc., thereby producing a single message with twice asmany bits for a group of two UEs.

Note that this process can be simplified by using a start-length or astart-end indication approach if the assigned subframes are adjacent.For example, a subframe allocation of 23, 24, 25 can be [23, 3] or [23,25].

This process of assigning subframes is simple and can be attractive ifthe number of UEs in a DMC group is low, e.g., two. However, when morethan two UEs are in a DMC group, there are some drawbacks, for example,the overhead can be high. For example, if 40 ms period is adopted forDMC group subframe allocations, then 40 bits are needed for oneindication of the subframes assigned to the group. If within the 40 ms,many subframes (e.g., 20) are assigned to a DMC group, then asub-bit-map of 20 bits is needed, which is a substantial overhead.

A Round-Robin (“RR”) process is another alternative to allocate DMC timeresources for a particular UE with less overhead. The allocation is madeover N repeating DMC subframes, and the number N, which sets the periodof the repeating DMC subframes, can be the same as or different from theDMC resource allocation period. Each UE is assigned one or more of a setof L parameters R₁, . . . , R_(L). If f is the DMC subframe index whichmeans renumbering subframes allocated for DMC from 0, 1, 2, 3, etc., theUE is allowed to transmit information on this subframe if there existsan integer i, iε{1, . . . , L}, for whichf mod N=R _(i),  Equation (1)where “mod” is the modulo operation for the period of the repeatingsubframes. On all other DMC subframes, the UE listens (receives).

An example of this resource allocation approach is as follows. If fourDMC UEs are in a group, and all have the same traffic requirements, thenthe number N of repeating DMC subframes can be set to 4. The first UEcan have an R value of R₁=0, the second can have an R value of R₂=1, thethird can have an R value of R₃=2, and the fourth can have an R value ofR₄=3. This way, each UE is allocated one subframe to transmitinformation every fourth DMC subframe, and listens on the other threeDMC subframes. When traffic is symmetric, a common N and only one Rvalue for each UE can be enough.

When traffic is asymmetric, different UEs can be assigned different Nvalues to adjust their respective period. For example, one UE amongthree can be assigned an N value of 2 and an R value of 0, so the UEtransmits in the first subframe every 2 DMC subframes. Another UE amongthe three can be assigned an N value of 4 and an R value of 1, so thatUE transmits information in the second subframe every 4 DMC subframes.The third UE among the three can be assigned the N value of 4 and an Rvalue of 3, so that UE transmits information in the fourth subframeevery 4 DMC subframes. Accordingly, a DMC subframe is uniquely andperiodically assigned to one of the three UEs.

Alternatively, there can be a common N value, and potentially plenty ofR values are needed. As a consequence, instead of providing a set ofindividual R values, there are other ways of providing the R values whenthere are multiple R values to lower overhead.

For example, a range of values [R₁, R₂] can be sent to a particular UEby start-length or start-end approaches.

A set of three values, R₀ for an initial R value, S_(t) for a stepvalue, and M for a number of R values, can be provided. The set of Rvalues is then determined by:R=R ₀ +k×S _(t) ,kε{0,M−1}.  Equation (2)

A combination of mechanisms can be used for resource allocation.

The subframe index f can be defined. For small values of R and N, itcould be the subframe index in a radioframe, or in a set of 40 subframes(such as what is done for an MBSFN configuration subframe), or thesubframe number within a DMC subframe period (e.g., if 10 subframes areassigned for DMC transmission, then the subframe number within theperiod is an integer from 0 to 9), or any other fixed value. However,this solution lacks flexibility, as explained earlier. A better solutionthat scales well with the number of users and degree of asymmetry is tocompute f as follows:f=10×[SF] _(i) +j,  Equation (3)where the subframe index SF_(i) is the radioframe index within asuperframe (e.g., SFi=0, . . . , 1023), and j is the subframe indexwithin the radioframe.

The message to send the parameters to the UEs can be a higher-layersignaling message, for example, an RRC message, and can be multicast orunicast.

Turning now to FIG. 4, illustrated is a flowchart of an embodiment of UEoperations to determine whether to transmit or receive information. Forillustrative purposes, it is assumed that Equation (1) is implementedbut a different equation can be used. The UE process begins in step orblock 410. In step or block 420, the UE determines the subframe index f.In step or block 430 the UE determines if Equation (1) is satisfied forone of its assigned R values. If Equation (1) is satisfied, in step orblock 440 the UE can transmit information on this subframe, and theprocess ends in step or block 470. If Equation (1) is not satisfied, instep or block 450 the UE receives information on this subframe, and theprocess ends in step or block 460. Thus, the UE is directed to receiveinformation when Equation (1) is not satisfied.

A Round-Robin solution can also be used to allocate time resources for aDMC group and the UEs in that group. For example, the start-end orstart-length method can be used to list all the resources for DMCtransmission within a certain period of time (10 ms, 40 ms, etc.). Thenthe UEs are listed corresponding to the resources.

For example, for a start-end method with a period of 10 ms, the timeresources are [3,4], [5,7], the corresponding UEs are [UE1, UE2]. Thus,UE1 is supposed to transmit information on the first group of timeresources, subframe 3 and 4, and UE2 is supposed to transmit informationon the second group of time resources, subframe 5, 6, and 7.

Another process employing predefined configurations is a thirdalternative and uses some type of signaling to indicate a predefinedconfiguration for the DMC group, similar to what is done in LTERelease-8 to indicate the uplink/downlink (“UL/DL”) subframeconfiguration. For instance, if it is signaled that a TDD configuration0 is used, it means for this predefined configuration that subframes 0and 5 are DL subframes, subframes 1 and 6 are special subframes, and theother subframes are UL subframes.

A similar solution could be used for DMC, with a pre-defined set ofconfigurations to indicate what mode the DMC UE has to use. Such anexample of a set of configurations is given in Table 1 belowillustrating examples of DMC subframe configurations that can beassigned to a particular UE, in accordance with an embodiment. In thisexample, the table indicates uplink resource allocation in an FDD mode.An entry “T” in the table means that the device transmits information ina DMC link, “R” means that the device receives information in a DMClink, and “C” means that the device is in a cellular mode. Note thatwhile only five configurations are shown, in practice, it is likely thatthere would be more.

TABLE 1 Examples of DMC Subframe Configurations Subframe index 0 1 2 3 45 6 7 8 9 configuration 0 T C C T R R T R R T configuration 1 T T C T RC T T R T configuration 2 T T T T C T T T T R configuration 3 T T T R TT T C T R configuration 4 T C C R R T C C R T

In Table 1, some subframes are denoted as being in a cellular mode. Suchsubframes may not need to be further described with the two-stepmessaging structure described earlier. A first message could indicatewith an index which subframes are used for DMC link, and the DMCsubframe configuration could be applied to those DMC subframes only. Inthat case, a small issue arises. The number of DMC subframes may vary,whereas such a table is of fixed length. In such a case, only the firstrows are used, or only the rows corresponding to the occupied subframesare used. Note also that Table 1 is defined for 10 subframes,corresponding to one radioframe. Other values, such as 40 could be used.

A TDD configuration of subframes of a group of predefined configurationscan thus be identified by an index for DMC use by a DMC group. Thepreset TDD binary pattern “1110000000” can indicate by an associatedindex that the first three subframes are used for the DMC link and theother seven are used for the cellular link. A second binary pattern,which can also be identified by an index, can be employed to identifywhich of the subframes assigned for DMC links are assigned to a first UEfor transmission, and which are assigned to the first UE for reception.For example, the binary pattern “110” can be used to communicate to thefirst UE that the first two DMC subframes are assigned to the first UEto transmit, and the third subframe for the first UE to listen.

The process introduced herein can be applied to any number of DMC UEs ina DMC group. However, the number of configurations grows with the numberof DMC UEs. As a consequence, this process may not be attractive formore than two DMC users. Two different RRC messages can be sent to theDMC UEs, or a single message can be multicast to the two DMC UEs. Inthat case, one UE has to interpret “T” as “R,” i.e., transmit asreceive. This can be done, e.g., by having the first UE interpret “T” as“T,” and the second UE interpreting “T” as “R.”

There are several benefits of this process. The mechanism simplifies DMCUE resource allocation by decomposing a complex procedure into anindication of opportunities for each individual UE, with implicitindication of non-transmit (i.e., receive) resources. A UE only needs toknow when to transmit; all the other DMC resources are receiveopportunities.

Further time resource allocation can be indicated by one message. Thereis no need to dynamically send two copies of one scheduling grant todifferentiate which UE is to transmit and which UE is to receive. Forexample, one scheduling grant identified by the group ID can betransmitted to the group of UEs to indicate the frequency resourceallocation, modulation and coding scheme “MCS,” and so on by physicallayer, the grant can be valid in following multiple subframes allocatedto the UE group.

Since a UE knows when it should receive a DMC transmission, it canprepare itself to receive that transmission.

In addition to knowing which subframes are assigned for transmission, itis also important to have a mechanism for the DMC UEs to indicate whereand when to receive. In particular, it is necessary to know when a givenHARQ process will be transmitted and/or acknowledged.

The HARQ process is a combination of forward error-correcting coding anderror detection using the Automatic Repeat reQest (“ARQ”) error-controlprocess. In standard ARQ, redundant (error detection) bits are added todata to be transmitted using an error-detecting code such as cyclicredundancy check (“CRC”). In HARQ, forward error correction (“FEC”) bits(such as a Reed-Solomon code, a convolutional code, or a Turbo code) areadded to the existing Error Detection (“ED”) bits to correct errors,while relying on ARQ to detect uncorrectable errors.

In practice, incorrectly received coded data blocks are often stored atthe receiver in a buffer rather than discarded, and when theretransmitted block is received, the stored and retransmitted blocks arecombined. This is called HARQ with soft combining. While it is possiblethat two given transmissions cannot be independently decoded withouterror, it may happen that the combination of the previously erroneouslyreceived transmissions provides enough information to correctly decode.There are two main soft combining methods in HARQ.

One soft-combining method is “chase combining,” wherein everyretransmission contains the same information (data and parity bits). Thereceiver can use maximum-ratio combining to combine the received bitswith the same bits from previous transmissions. In otherimplementations, log-likelihood ratios can be combined. Because alltransmissions are identical, chase combining can be seen as additionalrepetition coding. Essentially, each retransmission adds extra energy tothe received transmission and thereby increasing the signal-to-noiseratio (“E_(b)/N₀”).

Another soft-combining method is “incremental redundancy,” wherein everyretransmission contains information possibly different than the previousone. Multiple sets of coded bits are generated, each representing thesame set of information bits. The retransmission typically uses adifferent set of coded bits than the previous transmission, withdifferent redundancy versions generated by puncturing the encoderoutput. Thus, at every retransmission the receiver gains extra knowledgeand can increase the quality (e.g., signal-to-noise ratio) of somereceived values, e.g., log-likelihood ratios.

When the retransmission occurs at a fixed timing relative to the initialtransmission, the process is called synchronous HARQ. When theretransmission timing is more flexible, it is called asynchronous HARQ.When asynchronous HARQ is employed, it is necessary to identify theparticular HARQ transmission associated with a particular packet.Synchronous HARQ can simplify the HARQ procedure and save overhead.

In a conventional cellular mode, a UE maintains a certain number of itsown HARQ processes, for example up to 8 HARQ processes for a 3GPP LTEFDD UE to receive packets in parallel on the downlink, up to 8 HARQprocesses for a 3GPP LTE FDD UE to transmit packets in parallel on theuplink, up to 15 HARQ processes for a 3GPP LTE TDD UE to receive packetsin parallel on the downlink, and up to 8 HARQ processes for a 3GPP LTETDD UE to transmit packets in parallel on the uplink. It is noted thatthe two sets of HARQ processes of a UE for transmission and receptionare independent in the cellular mode. At the network side, thecommunications controller maintains a HARQ entity for each UE at itsmedia access control (“MAC”) layer, so multiple HARQ entities, eachentity having multiple HARQ processes for a UE, are simultaneouslymaintained by the communications controller.

In DMC mode, if a UE needs to manage a group of HARQ processes for eachpeer UE in a DMC group, the soft buffer requirements can be quite large.Each peer may potentially be the biggest data provider during a DMCsession, so it is neither good nor desirable to reduce the HARQ processnumber of any UE in advance. Furthermore, buffer preservation increasesin proportion to the number of DMC UEs in a DMC group.

Having the DMC UE operate like the communications controller withmultiple HARQ entities would require a lot of new functionalities, whichwould require drastic changes for both software and hardware.

In a cellular mode, at the physical layer, a UE does not know from wherethe data are originating. The UE just knows the data are sent from thecommunications controller. Identification of the source is left to ahigher layer. For DMC mode, this burden should not be imposed on a UE toknow the data sources in the physical layer as well. However, a DMC UEneeds to identify who is sending data in order to perform HARQ combiningif conventional HARQ is adopted. It is noted that each UE in the DMCgroup manages HARQ processes for the DMC link and HARQ processes for thecellular mode. Each UE configures its HARQ processes for the DMC linkand manages those processes using parameters provided by thecommunications controller. As a result, the HARQ processes for the DMClink and HARQ processes for the cellular mode are distinct andindependently determined. From a communications controller perspective,it does not use any HARQ processes for the DMC for communication.

A new HARQ protocol is introduced herein to perform HARQ in a DMC mode.

It is assumed that UE subframe allocation has already been performed,i.e., the subframes allocated for the DMC link and the subframesallocated for UE transmission over the DMC link. Extensions to otherresource allocation procedures are straightforward. An embodiment of aprocess lets the involved UEs share and maintain a common set of HARQprocesses for both transmission and reception of information that aretied to the timing of the commonly allocated DMC resources.

The process can be described as follows. Synchronous HARQ is assumed, sothe retransmission timing/subframes are predefined, but the intervalbetween the transmissions can be variable depending on the subframesallocated to the UE group. Each DMC subframe is allocated, implicitly orexplicitly, a HARQ process using parameters sent by the communicationscontroller. A way of allocating a HARQ process number is to signal themaximum number of HARQ processes to the UEs in the particular DMC group,to exclude all subframes not allocated to the particular DMC group, andto number the HARQ processes sequentially according to the allocatedsubframes.

Each UE in a DMC group maps one or more HARQ processes according to thesubframe number of the DMC subframes. The HARQ process numbers can bederived from the subframes allocated to the DMC group after the maximumnumber of HARQ processes is obtained from the communications controller.The maximum number of HARQ processes can be related to the number of UEsin the group, such as the maximum numbers of UEs in the group. Eachsubframe allocated to the DMC group will be mapped to a HARQ process nomatter which UE will transmit in the subframe. The maximum number ofHARQ processes can be derived from the communications controllerconfiguration, for example, the number of DMC subframes in a period ofDMC subframe/radio frame allocation. In one example, if four of everyten subframes are allocated for information (i.e., with a period of tensubframes) to a DMC group, e.g., subframes identified by the binarysequence “1100110000” which indicates that subframes zero, one, four,and five in each radio frame are allocated to the DMC group, then thetotal number of HARQ processes can be four and the HARQ process numbersassociated with the allocated DMC subframes could be zero, one, two, andthree. In this example, each UE of the group maps its group of HARQprocesses for the DMC link to the set of allocated subframes. It isnoted that the UE can have a same HARQ process number for the DMC linkand the cellular mode but those HARQ processes are determinedindependently. Or the maximum number of HARQ processes can be number ofsubframes in a period of DMC subframe/radio frame allocation minus one,herein is 3, then the HARQ process numbers associated with the allocatedDMC subframes could be zero, one, two, and one. Another example, if thetotal number HARQ processes are configured by higher layer (RRC layer)of eNB as H, where H is a positive integer, then the HARQ processnumbers associated with the allocated DMC subframes could be zero, one,two, . . . , (H−2), and (H−1). If H is 7, then the total HARQ processesassociated with DMC subframes will be 0, 1, 2, . . . , 5, and 6. Themaximum number of HARQ process can also be configured through controlchannel comprising PDCCH, ePDCCH, PBCH, and the like.

On each subframe when it is not transmitting, the UE receives, asdescribed previously hereinabove. Since the UE knows which HARQ processis transmitted on a given subframe, the UE can unequivocally performHARQ combining on any subframe in which it receives data.

Turning now to FIG. 5, illustrated is an example of the new HARQprocess, in accordance with an embodiment. A repeating pattern ofsubframes, 510, numbered 0, 1, 2, 3, . . . , 9, includes certainsubframes for DMC links, and certain subframes for cellularcommunication links. Subframes 0, 3, 5, 7, and 9 are allocated to agroup for DMC transmission, and are identified with crosshatching. Thesubframes broken out in the group 520 are sequentially associated with(mapped to) five HARQ process numbers, 0, 1, 2, 3, and 4. In the groupof four UEs 530 that form the DMC group, UE1, UE2, and UE4 have beenassigned, respectively, subframes 0, 3, and 9 for informationtransmissions. UE3 in the group 530 has been assigned subframes 5 and 7for information transmissions.

The five HARQ processes 540 are shown below each UE in the DMC group.Each UE is allocated one or more subframes for transmission and theaccordingly associated HARQ process to use to reconstruct received data.Each UE receives all the other HARQ processes of the associated subframein which it is not transmitting. UE1 does not need to employ HARQprocess 0 in the receiver to reconstruct data in subframe 0 because ittransmits in subframe 0. Accordingly, HARQ process 0 under UE1 is notcrosshatched. It is noted that UE1 must manage HARQ process 0 eventhough it is transmitting data for this process. Similarly, the HARQprocesses under the other UEs associated with their respectivetransmissions are not crosshatched.

Turning now to FIG. 6, illustrated is an embodiment of the correspondingcommunications controller operation. Note that this process would mostlikely run at the same time as the subframe allocation process. Theprocess begins in step or block 610. In step or block 620, thecommunications controller determines the maximum number of HARQprocesses it wants to transmit to the DMC group. The number can be sameas or different from the number of time resources assigned for DMC timeresource period. Note that these HARQ processes (for the DMC group) areindependent from the cellular HARQ processes, and do not share the sameHARQ pool of cellular HARQ processes. For instance, there might be aHARQ process number 1 for cellular operation, and another HARQ processnumber 1 for a specific DMC group operation. In step or block 630, thecommunications controller can transmit to the DMC group the maximumnumber of HARQ processes allocated to this group if the number of HARQprocesses is different from the number of time resources assigned forDMC time resource period. The communications controller may not need toinform UEs explicitly of the maximum number of HARQ process if thenumber of the HARQ processes is same as the number of time resourcesassigned for DMC time resource period. An option for this signaling isRRC signaling. Note that the number of HARQ processes could also bejointly sent with the subframe allocation process. The process ends instep or block 640.

Turning now to FIG. 7, illustrated is a flowchart of an embodiment of UEoperations when the UE in a DMC group receives the HARQ signalingincluding information about the maximum number of HARQ processes. In anembodiment, the UE can just assume the number of the HARQ processes forDMC is the same as the number of the time resources in DMC time resourceperiod. The process begins in step or block 710. In step or block 720the UE gets the (maximum) number of HARQ processes from thecommunications controller. In step or block 730, depending on the numberof HARQ processes and the allocation of subframes to the DMC group, theUE determines which specific HARQ process is associated to a particularsubframe by sequentially associating the HARQ processes to the subframesassigned to the DMC group. The UE then associates the HARQ processescorresponding to all the subframes assigned to the DMC group. Theprocess ends in step or block 740.

Turning now to FIG. 8, illustrated is a flowchart of an embodiment of UEoperations on a given subframe. On all the subframes where the UE doesnot transmit information on the DMC link, it receives information on theDMC link and updates the corresponding HARQ process. The operationsillustrated in FIG. 8 are performed after those illustrated in FIG. 7.

If a UE is added to the group or leaves the group, communicationscontroller may need to reconfigure time resource allocation and the HARQprocess allocation as well.

The process begins in step or block 810. In step or block 820, the UEdetermines whether to transmit on the current subframe on the DMC link.The UE receives from the communications controller a set of subframesfor transmission on DMC link. If the UE determines it is time totransmit, in step or block 860 the UE transmits information in thesubframe associated to a HARQ process. The process ends in step or block870. If the UE determines in step or block 820 that it does not transmitinformation in the current subframe, then in step or block 830, the UEreceives information over the DMC link in the current subframeassociated with the HARQ process. The allocated DMC subframes not usedfor transmission over the DMC link can be receiving DMC transmissionsover the DMC link. In step or block 840 the UE updates the buffer ofthis corresponding HARQ process. The process ends in step or block 850.

With this operation, the new data indicator (“NDI”) bit of the currentpacket can be used to indicate how the receiver should combine thecurrent data packet with previous version(s). If the NDI indicates thepacket is an initial transmission, the UE empties the buffer of thecorresponding HARQ process. If the UE does not decode the newly-receivedpacket correctly, it buffers the newly-received packet(s); if the NDIindicates the packet is retransmission, the UE combines thenewly-received packet with previously received versions in the HARQprocess buffer. The NDI bit can be sent together with its correspondingdata, but coded separately so that the involved UEs can first decide tocombine newly-received packet with previously received versions in theHARQ process buffer, or just discard the old packet version.

There are several benefits of this process. A UE can receive data,combine packages of initial transmissions and retransmissions, anddecode the data packets before knowing the source for the data. It isassumed here that the scrambling and reference signal sequence group isthe same within a DMC group which can be identified or defined by thegroup ID. The receiver can then just blindly combine the data packetsaccording to the subframe number. There is no necessity to have thephysical layer know the identity of the source. With an assumption ofone HARQ process per time resource, the memory needed in DMC mode can beanticipated in advance. In general, the amount of memory needed for a UEin DMC mode is much less than the communication controller's requirementfor uplink transmissions, where the amount of memory is related to thenumber of active UEs and the number of HARQ processes per UE. Thefeedback can also be tied to timing.

More than one packet can be transmitted in one HARQ process, so multipleacknowledgement/negative acknowledgement (“ACK/NACK”, “A/N”) bits can befed back; for simplicity, in the following text, one packet is used, andACK/NACK feedback is used to denote the whole feedback for a HARQprocess. For sending a HARQ ACK/NACK, after a UE receives a packet, ittakes a certain period of time, the HARQ processing time, to process thepacket and prepare the corresponding ACK/NACK feedback. The ACK/NACKfeedback corresponding to a HARQ process for a packet cannot beavailable and be sent, before the processing time is complete. For LTE,the processing time should not be more than four subframes (4 ms).

In the cellular mode, a packet received by a UE on the DL must beacknowledged to the communications controller on a predefined subframeon the UL. In FDD mode, a DL packet is acknowledged four subframes afterbeing received. In TDD mode, a DL packet is allocated to the first ULsubframe at least four subframes after the DL packet has been received.It is noted the ACK/NACK feedback for the cellular mode is determinedindependently and performed separately from the ACK/NACK feedbackbetween a group of two or more UEs in the DMC mode.

For the DMC mode, the UEs can operate in a half-duplex manner. Receivingand transmitting are not performed simultaneously. If dedicatedindependent ACK/NACK feedback opportunities are assigned to UEs for theHARQ processes on the DMC link, the ACK/NACK overhead will consumeresources available for information transmission. Furthermore, it alsocomplicates the higher layer configuration for transmission timing. Inan embodiment, the ACK/NACK feedback is grouped with, and accompanies, ainformation transmission. The ACK/NACK feedback can be encoded with, orseparately from, the data. In an embodiment, the ACK/NACK feedback isencoded separately from the data. In this manner, a UE feeds backACK/NACK when it has an opportunity to transmit data. This ACK/NACKfeedback is transmitted on the DMC link. Since several HARQ processescan be ACK/NACKed together, some mapping rules are employed for DMC UEs.

In a first example, retransmission of the original data occursautomatically without ACK/NACK feedback.

If a set of ACK/NACKs is to be fed back, the overhead of thecorresponding HARQ process number could be large, which wastes resourcesand degrades the decoding performance of the data channel (packet).Discarding ACK/NACK feedback could be one solution. In this case thetransmitter just retransmits according to a predetermined maximum numberof retransmissions. This solution can be efficient for transmission ofsmall packets. However, for transmission of large packets, it is highlyinefficient since unnecessary retransmissions may occur quitefrequently.

In a second example the corresponding HARQ process number is providedwith the ACK/NACK feedback explicitly. This solution ensures HARQprocesses are correctly identified and acknowledged. The correspondingHARQ process number of an ACK/NACK feedback is explicitly indicated sothat the packet source/transmitter can know if a given packet wascorrectly received in that particular subframe (which can be uniquelytied to a HARQ process, as described previously hereinabove).

Turning now to FIG. 9, illustrated is a graphical representation ofACK/NACK feedback with explicit indication of the corresponding HARQprocess number, in accordance with an embodiment. A periodic pattern often subframes is indicated with reference number 910. Five subframes,which is an example number, in the periodic sequence 910 that areallocated to a group of UEs for DMC are crosshatched. The communicationcontroller allocates this set of subframes for the DMC link and signalsthe set to the group of UEs. The subframes allocated for DMC aresequentially repeated in the group of subframes indicated with referencenumber 920. ACK/NACK feedbacks from the DMC UEs, indicated withreference number 930, provide the HARQ process numbers and theassociated ACK/NACK feedbacks. The UE transmitting an ACK/NACK feedbackin the crosshatched subframes acknowledges the received packets thatwere previously received, taking into account processing time. Asillustrated by the ACK/NACK feedbacks indicated with reference number930, the UE transmitting an ACK/NACK response indicates the HARQ processnumber being ACK/NACKed in addition to the actual ACK/NACK feedbackfield.

Turning now to FIG. 10, illustrated is an embodiment of a processperformed at a UE for sending ACK/NACK and generating ACK/NACK for aHARQ process. The process begins in step or block 1010. In step or block1020, the UE determines if it is supposed to transmit over the DMC linkin the current subframe. The set of subframes for transmission over theDMC link is signaled to the UE by the communications controller. If itis not, in step or block 1030 it attempts to receive and decode thepacket over the DMC link, potentially performing HARQ combining for aretransmission, and assessing whether the packet was correctly received.In step or block 1040, it records the ACK/NACK status for this HARQprocess and the HARQ process number corresponding to the currentsubframe and stores the information to a list. The process then ends instep or block 1050. If in step or block 1020 the UE is to transmit inthis subframe, in step or block 1060 the UE aggregates the contents ofthe list and transmits the aggregated ACQ/NACK feedback, and in step orblock 1070 clears the list. It is noted that the UE generates anacknowledgement for its HARQ process (for its transmission) on thissubframe. It is further noted that the UE can transmit data while it istransmitting the aggregated ACK/NACK feedback. The process ends in stepor block 1050.

Turning now to FIG. 11, illustrated is an embodiment of UE operation toassess if a packet was correctly received by the other UEs in a DMCgroup by examining the received ACK/NACK feedback. The process begins instep or block 1110. It is assumed that the UE is monitoring ACK/NACK forHARQ process “i.” In this example, the UE transmitted a packet over theDMC link for HARQ process i. In step or block 1120, in a receivedsubframe, the UE monitoring ACK/NACK for HARQ process i collects andstores the aggregated ACK/NACK feedback sent by the UE transmitting inthat particular subframe. In step or block 1130, the UE retrieves frommemory the aggregated ACK/NACK feedback corresponding to HARQ process iassociated with this particular subframe, as well as in previoussubframes. In step or block 1140, the UE then assesses if an ACK/NACKfeedback of HARQ process i originating from UEs transmitting on all HARQprocesses except i have been received. If not, in block or step 1150 theUE waits for the next subframe to collect more ACK/NACK responses. Ifyes, in step or block 1170 the UE checks if the received ACK/NACK fromall HARQ processes were positive ACKs. If yes, in step or block 1190 thepacket is identified as having been correctly received by all thereceiving UEs. If not, in step or block 1180 the packet is identified asnot having been correctly received, and the UE then initiates the HARQretransmission procedure. The process ends in step or block 1160.

Note that the process might be altered slightly. For instance, if one UEreports that the packet was incorrectly received, the UE that originallytransmitted the packet decides to retransmit the packet for HARQ processi before having received feedback from all HARQ processes, because atleast one receiving UE was not able to correctly decode the packet.

In a third example, an embodiment employing sequential feedback reportsa sliding window of DMC subframes for which ACK/NACK feedbacks will beprovided. This process does not require explicitly sending the HARQprocess number with the aggregated ACK/NACK feedback. This process ismore systematic and can be simpler to implement. It can reduce ACK/NACKfeedback overhead.

The third example is described as follows. A sliding window of length Nfor ACK/NACK feedback of each UE in a DMC group is set, e.g., by thenetwork. The length N can represent a number of subframes. The slidingwindow length can be the same as or smaller than the number of allocatedsubframes for the DMC link or the maximum number of HARQ processes. Allof the UEs in the DMC group know the sliding window length, which iseither pre-configured by communications controller, or communicated byhigher layer (RRC) signaling from the communications controller. When agiven UE is to transmit, the UE transmits the aggregated ACK/NACK(s) forall N previously received HARQ processes/packages within the window. Theaggregated ACK/NACK feedback can be multiplexed, such as using a bitmap,with a bit (or several bits) corresponding to a given HARQ process, andsequenced according to the DMC subframes in the sliding window. Forinstance, the first bit could correspond to the earliest subframe in thesliding window, and the last bit to the last subframe. Other sequencingarrangements can be employed. The aggregated ACK/NACK feedback canemploy bundling, where feedback for all ACK/NACK processes within thewindow are logically ANDed together, similar to the bundling process inthe time division duplex mode of LTE.

In addition, if within the window, there is a subframe or subframeswhere the UE transmits a packet or packets, and accordingly does notrequire feedback, the corresponding feedback for the packet(s) can justbe an ACK(s).

The ACK/NACK feedback and other control information can be coded by aconventional linear block code, so the mapping from ACK to binary 0 willnot degrade decoding performance.

Turning now to FIGS. 12 and 13, illustrated is a graphicalrepresentation of ACK/NACK reporting with a sliding window for a firstcase and a second case, respectively, in accordance with an embodiment.UE operations have some similarities to the example described above forthe second HARQ example, wherein explicit feedback of the HARQ processnumber is acknowledged, the difference now being updating by using abitmap containing aggregated ACK/NACK feedbacks corresponding tosubframe positions in the sliding window. The association of an ACK/NACKfeedback with a HARQ process can be sequential, e.g., the first ACK/NACKresponse can be associated with the first subframe in the slidingwindow, or the association can be specified by a table.

The cases illustrated in FIGS. 12 and 13 illustrate the number ofallocated subframes for DMC is 5 for given time resource period and asliding window length of 5. In the example illustrated in FIG. 12, thereis sufficient separation (processing time of 4 subframes) betweensubframes transmitting data in the sliding window (which corresponds tosubframe #9 of 1210) and the subframe 1270 (which corresponds tosubframe #13 of 1210) for ACK/NACK feedback after the sliding window1240, but in the example illustrated in FIG. 13, there is insufficientseparation of 2 subframes between the subframe ahead of 1370 (whichcorresponding to subframe #3 of 1310) and subframe 1370 (whichcorresponds to subframe #5 of 1310) for ACK/NACK feedback, so thesliding window 1340 cannot include the A/N for that subframe,illustrated by the double-headed arrow 1370. The collective cellular andDMC subframes in a frame are indicated by reference numerals 1210, 1310.The DMC subframe allocation for the engaged UEs in a DMC group isindicated by the crosshatched subframes in the frame 1210, 1310 (thesubframe numbers are shown above 1210, 1310), and further by theperiodic grouping of DMC subframes indicated reference numerals 1220,1320. The DMC subframes allocated to a DMC UE in the group are shown bydotted boxes, among those illustrated by reference numerals 1220, 1320.The DMC UE is allocated two subframes for transmission (and theircorresponding HARQ processes) in a time resource period, labeled assubframes “1” and “2” in FIGS. 12 and 13. The subframes to be ACKed arethe ones in the sliding windows 1240, 1340. ACK/NACK feedback and itscorresponding subframe are indicated by the double-headed arrows, suchas by the double-headed arrows 1260 and 1360. ACK/NACK feedbacks for thesubframes identified by the numerals 1 and 2 allocated to the UE amongthe engaged UEs in the DMC group is indicated among the feedbacks 1230and 1330 only by an “A”, or “N”, not an “A/N,” since this feedback isfrom a transmitting UE to itself, and the “A” or “N” is just aplaceholder to keep the order of the feedbacks in the bitmap. Withoutloss of generality, an acknowledgement (“A”) is used as a placeholder.The period of a frame 1210, 1310 is at fourteen subframes in thisexample, and the length of the sliding windows 1240, 1340 is five,indicated by the double-headed, horizontal arrows, for example by thedouble-headed, horizontal arrows 1250 and 1350.

The process can be further enhanced. If most of the DMC subframes oreven all the DMC subframes are assigned to one UE, the UE has morechances to transmit, which means it has more chances to feed backACK/NACKs. This can create a waste of resources since the same ACK/NACKcan be reported multiple times. At the expense of a slightly morecomplex process at the receiver, the previously reported ACK/NACK mightbe omitted from future reports, though this makes the bitmap fieldlength variable.

For a DMC group with 2 UEs, the ACK/NACKs can be easily fed back at thereception UE's first available transmitting chance, and then nottransmitted any more. The feedback timing can be simplified. Forexample, the subframes carrying feedbacks can be configuredsemi-statically or can be dynamically signaled. Beside these subframes,no ACK/NACK will be transmitted.

Spatial domain bundling and time domain bundling as in a TDD system canalso be used.

Several mechanisms related to the time resource allocation for a DMCgroup have been described. The covered aspects include a subframeallocation process, a HARQ timeline, and HARQ ACK/NACK reporting.

Referring now to FIG. 14, illustrated is a block diagram of elements ofa processing system 1400 that can be used to perform one or more of theprocesses discussed hereinabove. One or more of the elements illustratedin FIG. 14 may not be necessary in a particular embodiment. For example,a user equipment may not comprise a mouse. The processing system 1400comprises a processor 1410 equipped with one or more input/outputdevices, such as a mouse, a keyboard, a printer, or the like, and adisplay. The processor 1410 includes a central processing unit (CPU),memory, a mass storage device, a video adapter, a network interface, andan I/O interface connected to a bus 1420.

The bus 1420 can be one or more of any type of several bus architecturesincluding a memory bus or memory controller, a peripheral bus, videobus, or the like. The CPU can comprise any type of electronic dataprocessor. The memory can comprise any type of system memory such asstatic random access memory (SRAM), dynamic random access memory (DRAM),synchronous DRAM (SDRAM), read-only memory (ROM), non-volatile RAM(“NVRAM”), a combination thereof, or the like. In an embodiment, thememory can include ROM for use at boot-up, and DRAM for data storage foruse while executing programs.

A transceiver 1430 coupled to an antenna 1440 is coupled to the bus 1420to provide a wireless transmitting and receiving function for theprocessing system. For example, without limitation, the transceiver 1430can provide a wireless transmitting and receiving function for acellular communication network.

The mass storage device can comprise any type of storage deviceconfigured to store data, programs, and other information and to makethe data, programs, and other information accessible via the bus. Themass storage device can comprise, for example, one or more of a harddisk drive, a magnetic disk drive, an optical disk drive, a remote disk,or the like.

The video adapter and the I/O interface provide interfaces to coupleexternal input and output devices to the processor. Examples of inputand output devices include the display coupled to the video adapter andthe mouse/keyboard/printer coupled to the I/O interface. Other devicescan be coupled to the processor, and additional or fewer interface cardscan be utilized. For example, a serial interface card (not shown) can beused to provide a serial interface for a printer.

The processor also preferably includes a network interface, which can bea wired link, such as an Ethernet cable or the like, and/or a wirelesslink to enable communication with a network such as a cellularcommunication network. The network interface allows the processor tocommunicate with remote units via the network. In an embodiment, theprocessor is coupled to a local-area network or a wide-area network toprovide communications to remote devices, such as other processors, theInternet, remote storage facilities, or the like.

It should be noted that the processing system can include othercomponents. For example, the processing system can include powersupplies, cables, a motherboard, removable storage media, cases, and thelike. These other components, although not shown, are considered part ofthe processing system.

Although embodiments described hereinabove operate within thespecifications of a cellular communication network such as a 3GPP-LTEcellular network, other wireless communication arrangements arecontemplated within the broad scope of an embodiment, including WIMAXwireless communications systems, GSM, WI-FI wireless communicationssystems, and other wireless communication systems.

It is noted that, unless indicated otherwise, functions described hereincan be performed in either hardware or software, or some combinationthereof, with or without human intervention. In an embodiment, thefunctions are performed by a processor such as a computer or anelectronic data processor, such as that discussed hereinabove withreference to FIG. 14, in accordance with code such as computer programcode, software, and/or integrated circuits that are coded to performsuch functions, unless indicated otherwise.

Embodiments such as those presented herein provide a system and a methodfor operating a communications controller. For example, embodimentsprovide a system constructed with a transceiver and a processor coupledto the transceiver. The processor in conjunction with the transceiver isconfigured to allocate a first set of subframes to a group of UEs for aDMC link, allocate a second set of subframes to a particular UE in agroup of UEs, transmit a first message including information about thefirst set of subframes to the group of UEs, and transmit a secondmessage including information about the second set of subframes to theparticular UE. In an embodiment, the second set of subframes is a subsetof the first set of subframes, the information about the second setincludes subframes in which the particular UE may transmit to other UEsin the group of UEs, and subframes in the first set not in the secondset are allocated for reception by the particular UE. In an embodiment,the first message and the second message are transmitted in a singlemessage. In an embodiment, the first message is transmitted in a radioresource control signaling message. In an embodiment, the first messageis transmitted on a control channel. In an embodiment, the secondmessage is transmitted on a radio resource control channel. In anembodiment, the second message is transmitted on a control channel. Inan embodiment, the first message transmitted to the group of UEs isaddressed to all UEs in the group of UEs. In an embodiment, a bitmapmessage is employed to identify the first set of subframes and thesecond set of subframes. In an embodiment, a first bitmap field of thebitmap message is employed to identify the first set of subframes and asecond bitmap field of the bitmap message is employed to identify thesecond set of subframes. In an embodiment, the second bitmap field is ofdifferent length than the first bit map field. In an embodiment, afunction depending on at least a subframe index I is used to determineif a subframe of the index I is within the second set. An embodimentfurther includes assigning a parameter M and a parameter R to theparticular UE in the group of UEs for the function, wherein the subframeof index I is assigned to the particular UE in the group to transmit ifI mod M=R. An embodiment further includes assigning at least anadditional parameter R to the particular UE in the group. In anembodiment, the subframe of the index I is indexed depending on itsposition in the first set. In an embodiment, a predefined configurationof subframes is employed to indicate the first set of subframes and thesecond set of subframes for transmission by the particular UE in thegroup. In an embodiment, a subframe in the first set not in the secondset is employed for reception by the particular UE of the group. Anembodiment further includes transmitting the first message to the groupof UEs to identify the first set of subframes and the second message tothe particular UE of the group to identify the second set of subframesfor transmission by the particular UE. In an embodiment, the group ofUEs is identified by a group identifier. In an embodiment, each UE ofthe group is referenced by a unique UE identifier within the group.

Further embodiments provide a system and a method for operating a userequipment. For example, embodiments can provide a system constructedwith a transceiver and a processor coupled to the transceiver. Theprocessor in conjunction with the transceiver is configured to receive afirst message including information about a first set of subframes for agroup of UEs for a DMC link, and receive a second message includinginformation about a second set of subframes assigned to the particularUE. In an embodiment, the second set of subframes is a subset of thefirst set of subframes, the information about the second set includessubframes in which the UE may transmit in the DMC link to other UEs inthe group, and subframes in the first set not in the second set areallocated for reception by the UE. A subframe in the first set not inthe second set allocated for reception by the UE can be allocated toanother UE for transmission. In an embodiment, the first message and thesecond message are received in a single message. In an embodiment, thefirst message is received in a radio resource control signaling message.In an embodiment, the first message is received on a control channel,such as a PDCCH. In an embodiment, the second message is received on aradio resource control channel. In an embodiment, the second message isreceived on a control channel, such as a PDCCH. In an embodiment, thefirst message is directed to all UEs in the group. In an embodiment, abitmap message is employed to identify the first set of subframes andthe second set of subframes. In an embodiment, a first bitmap field ofthe bitmap message is employed to identify the first set of subframesand a second bitmap field of the bitmap message is employed to identifythe second set of subframes. In an embodiment, the second bitmap fieldis of different length than the first bitmap field. In an embodiment, afunction depending on at least a subframe index I is used to determineif a subframe of the index I is within the second set. In a furtherembodiment, receiving a transmission including a parameter M and aparameter R, the subframe of index I is allocated to the UE if I modM=R. A further embodiment includes receiving at least an additionalparameter R. In an embodiment, the subframe index I is indexed dependingon its position in the first set. In an embodiment, a predefinedconfiguration of subframes is employed to identify the first set ofsubframes and the second set of subframes. A further embodiment includesreceiving a first message addressed to the group of UEs to identify thefirst set of subframes and a second message addressed to the UE toidentify the second set of subframes for transmission by the UE in theDMC link. In an embodiment, the group of UEs is identified by a groupidentifier. In an embodiment, the UE within the group is identified by aUE identifier.

Further embodiments provide a system and a method for operating acommunications controller for a DMC link for a group of user equipments.For example, embodiments provide a system constructed with a transceiverand a processor coupled to the transceiver. The processor in conjunctionwith the transceiver is configured to allocate a set of subframes in oneperiodic group of subframes to the group of UEs, signal the allocatedset of subframes to the group of UEs, and transmit parameters related toa group of HARQ processes of the DMC link. In an embodiment, thecommunication controller uses HARQ processes for cellular UEtransmission that are determined independently from HARQ processes ofthe group of HARQ processes for the DMC link, and the parameters areconfigured to enable the group of UEs to manage the group of HARQprocesses for the DMC link. In an embodiment, the parameters related tothe group of HARQ processes for the DMC link include a maximum number ofHARQ processes. In an embodiment, the maximum number of HARQ processesis derived from at least a number of UEs in the group of UEs. In anembodiment, the maximum number of HARQ processes is derived from atleast a number of subframes within the set of allocated subframes. In anembodiment, the maximum number of HARQ processes is equal to the numberof subframes within the set of allocated subframes. In an embodiment,the maximum number of HARQ processes is derived from at least aconfiguration of the communications controller. In an embodiment, themaximum number of HARQ processes is derived from at least a number ofsubframes within the one periodic group of the allocated subframes. Inan embodiment, a first HARQ process in the group of HARQ processes ofthe DMC link corresponds to a first subframe of the set of allocatedsubframes allocated to the group of UEs. In an embodiment, the HARQprocesses of the DMC link are numbered according to the subframesallocated for the group of UEs. In an embodiment, the numbering issequential. In an embodiment, the transmitting the parameters related tothe group of HARQ processes is transmitted in a radio resource controlsignaling message. In an embodiment, the transmitting the parametersrelated to the group of HARQ processes of the DMC link is transmitted ina control channel.

Further embodiments provide a system and a method for operating a UE fora DMC link for a group of user equipments. For example, embodimentsprovide a system constructed with a transceiver and a processor coupledto the transceiver. The processor in conjunction with the transceiver isconfigured to receive from a communications controller an allocation ofa first set of subframes for a group of UEs for a DMC link, and receivefrom the communications controller parameters related to a group of HARQprocesses of the DMC link. In an embodiment, the UE manages a group ofHARQ processes of a cellular UE transmission and at least one HARQprocess from the group of HARQ processes of the DMC link, and the UEmaps the at least one HARQ process from the group of HARQ processesbased on the allocation of the first set of subframes and the receivedparameters. In an embodiment, the mapping of the at least one HARQprocess includes mapping all HARQ processes from the group of HARQprocesses of the DMC link. In an embodiment, a process number of a HARQprocess from the group of HARQ processes of the cellular UE transmissionis equal to a process number of a HARQ process from the group of HARQprocesses of the DMC link. A further embodiment includes receiving anallocation of a second set of subframes from the communicationscontroller wherein the allocated second set of subframes is a subset ofthe allocated first set of subframes, and wherein the UE may transmit inthe allocated second set of subframes. In an embodiment, thetransmitting uses the mapped at least one HARQ process from the group ofHARQ processes. In an embodiment, the UE receives on the allocated firstset of subframes that are not part of the allocated second set. Afurther embodiment includes receiving from another UE within the groupof UEs in a subframe from the allocated first set of subframes using themapped at least one HARQ process from the group of HARQ processes. Afurther embodiment includes transmitting a New Data Indicator bit. In anembodiment, the mapping of the at least one HARQ process from the groupof HARQ processes is sequential to the allocated first set of subframes.In an embodiment, the receiving the parameters related to the group ofHARQ processes of the DMC link is received in a radio resource controlsignaling message. In an embodiment, the receiving the parametersrelated to the group of HARQ processes of the DMC link is received in acontrol channel. In an embodiment, the parameters related to the groupof HARQ processes of the DMC link include an indication of a maximumnumber of the group of HARQ processes of the DMC link.

Further embodiments provide a system and a method for operating acommunications controller for a DMC link for a group of user equipments.For example, embodiments provide a system constructed with a transceiverand a processor coupled to the transceiver. The processor in conjunctionwith the transceiver is configured to allocate a set of subframes to thegroup of UEs for the DMC link, signal the set of allocated subframes tothe group of UEs, and signal a length of a sliding window to the groupof UEs. In an embodiment, UEs of the group of UEs aggregateacknowledgment and negative acknowledgement (“ACK/NACK”) feedback forcommunications over the DMC link according to the length of the slidingwindow. In an embodiment, the ACK/NACK feedback for the communicationsover the DMC link is determined independently from ACK/NACK feedback forcellular transmission between the communication controller and the groupof UEs. In an embodiment, the length of the sliding window is a numberof subframes. In a further embodiment, the length of the sliding windowis determined from the allocated set of subframes. In a furtherembodiment, parameters related to a group of HARQ processes of the DMClink are signaled to the group of UEs. In an embodiment, the ACK/NACKfeedback for communications over the DMC link is for the group of HARQprocesses of the DMC link. In an embodiment, the signaling the length ofthe sliding window to the group of UEs is transmitted in a radioresource control signaling message.

Further embodiments provide a system and a method for operating a UE fora DMC link for a group of user equipments. For example, embodimentsprovide a system constructed with a transceiver and a processor coupledto the transceiver. The processor in conjunction with the transceiver isconfigured to generate ACK/NACK feedback for a group of HARQ processesover the DMC link, aggregate the ACK/NACK feedback according to a lengthof a sliding window and an allocation of a first set of subframes forthe DMC link received from a communication controller, and transmit theaggregated ACK/NACK feedback to other UEs in the group of UEs of the DMClink on a subframe from an allocation of a second set of subframesreceived from the communications controller. In an embodiment, theallocation of the second set of subframes is a subset of the allocationof the first set of subframes. In an embodiment, the aggregating theACK/NACK feedback includes identifying subframes that include thesliding window. In an embodiment, the subframes that include the slidingwindow include subframes from the allocation of the first set ofsubframes. In an embodiment, the identifying the subframes that includethe sliding window accounts for processing time of processing data overthe DMC link. In a further embodiment, HARQ processes of the group ofHARQ processes are associated to the identified subframes that includethe sliding window. In an embodiment, the aggregating the ACK/NACKfeedback includes bundling of ACK/NACK feedback for the associated HARQprocesses of the group of HARQ processes. In an embodiment, theaggregating the ACK/NACK feedback includes multiplexing of ACK/NACKfeedback for the associated HARQ processes of the group of HARQprocesses. In an embodiment, the length of the sliding window isreceived from the communications controller. In an embodiment, theaggregated ACK/NACK feedback is determined independently from ACK/NACKfeedback for cellular transmission between the communications controllerand the group of UEs. In an embodiment, the UE receives transmission ofother aggregated ACK/NACK feedback on a subframe of the allocation ofthe first set of subframes that is not part of the allocation of thesecond set of subframes. In an embodiment, the transmitting theaggregated ACK/NACK feedback further includes transmitting data. In anembodiment, the generating the ACK/NACK feedback further includesgenerating an acknowledgement for HARQ processes transmitted on theallocation of the second set of subframes.

While this invention has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various modifications and combinations of theillustrative embodiments, as well as other embodiments of the invention,will be apparent to persons skilled in the art upon reference to thedescription. It is therefore intended that the appended claims encompassany such modifications or embodiments.

What is claimed is:
 1. A method of operating a communications controllerfor a direct mobile communication (“DMC”) link for a group of userequipments (“UEs”), the method comprising: allocating a set of subframesin one periodic group of subframes for the group of UEs; allocating, bythe communication controller, a subset of the set of subframes for a UEin the group of UEs, wherein the UE is allowed to transmit informationin the subset of the set of subframes, but not in remaining subframes ofthe allocated set of subframes; signaling the allocated set of subframesand the allocated subset of the set of subframes; and transmitting oneor more parameters, wherein the one or more parameters are related to agroup of Hybrid Automatic Repeat reQuest (“HARQ”) processes for the DMClink, wherein the communication controller uses HARQ processes forcellular UE transmission that are performed independently from HARQprocesses of the group of HARQ processes for the DMC link, wherein theone or more parameters, including a group identifier parameter, areconfigured to enable the group of UEs to maintain the group of HARQprocesses for the DMC link; and wherein the group of HARQ processes forthe DMC link are allocated by the communications controller.
 2. Themethod as recited in claim 1, wherein the one or more parameters relatedto the group of HARQ processes for the DMC link comprise a maximumnumber of HARQ processes.
 3. The method as recited in claim 2, whereinthe maximum number of HARQ processes is derived from at least a numberof UEs in the group of UEs.
 4. The method as recited in claim 2, whereinthe maximum number of HARQ processes is derived from at least a numberof subframes within the set of allocated subframes.
 5. The method asrecited in claim 2, wherein the maximum number of HARQ processes isderived from at least a configuration of the communications controller.6. The method as recited in claim 1 wherein a first HARQ process in thegroup of HARQ processes of the DMC link corresponds to a first subframeof the set of subframes allocated to the group of UEs.
 7. The method asrecited in claim 1 wherein the HARQ processes of the DMC link areidentified according to the subframes allocated for the group of UEs. 8.The method as recited in claim 7 wherein the identification issequential.
 9. The method as recited in claim 1 wherein the transmittingthe one or more parameters related to the group of HARQ processes istransmitted in a radio resource control signaling message.
 10. Themethod as recited in claim 1 wherein the transmitting the one or moreparameters related to the group of HARQ processes of the DMC link istransmitted using one or more of a higher layer signaling and a controlchannel.
 11. A method of operating a user equipment (“UE”), the methodcomprising: receiving from a communications controller an allocation ofa first set of subframes for a group of UEs for a direct mobilecommunication (“DMC”) link; receiving from the communications controlleran allocation of a subset of the set of subframes for the UE, whereinthe allocated subset of the set of subframes is a subset of theallocated first set of subframes, and wherein the UE is allowed totransmit information in the allocated subset of the set of subframes,but not in remaining subframes of the allocated first set of subframes;and receiving, from the communications controller, one or moreparameters related to a group of Hybrid Automatic Repeat reQuest(“HARQ”) processes of the DMC link, wherein the UE maintains a group ofHARQ processes of a cellular UE transmission and at least one HARQprocess from the group of HARQ processes of the DMC link, wherein the atleast one HARQ process is performed independently from the group of HARQprocesses of the cellular UE transmission, and wherein the UE maps theat least one HARQ process from the group of HARQ processes of the DMClink based on the allocated first set of subframes and the received oneor more parameters, including a group identifier parameter.
 12. Themethod as recited in claim 11 wherein the mapping of the at least oneHARQ process comprises mapping all HARQ processes from the group of HARQprocesses of the DMC link.
 13. The method as recited in claim 11,wherein a process number of a HARQ process from the group of HARQprocesses of the cellular UE transmission is equal to a process numberof a HARQ process from the group of HARQ processes of the DMC link. 14.The method as recited in claim 11 wherein the UE allowed to transmitinformation in the allocated subset of the set of subframes comprisesthe UE using the mapped at least one HARQ process from the group of HARQprocesses.
 15. The method as recited in claim 11 wherein the UE receivesinformation on the allocated first set of subframes that are not part ofthe allocated subset of the set of subframes.
 16. The method as recitedin claim 11 further comprising receiving information from another UEwithin the group of UEs in a subframe from the allocated first set ofsubframes using the mapped at least one HARQ process from the group ofHARQ processes.
 17. The method as recited in claim 11 further comprisingtransmitting a New Data Indicator bit.
 18. The method as recited inclaim 11 wherein the mapping of the at least one HARQ process from thegroup of HARQ processes is sequential to the allocated first set ofsubframes.
 19. The method as recited in claim 11 wherein the receivingthe one or more parameters related to the group of HARQ processes of theDMC link is received in a radio resource control signaling message. 20.The method as recited in claim 11 wherein the one or more parametersrelated to the group of HARQ processes of the DMC link comprise anindication of a maximum number of the group of HARQ processes of the DMClink.
 21. A communications controller, comprising: a transceiver; and aprocessor unit coupled to the transceiver, the processor unit, inconjunction with the transceiver, configured to cause the communicationscontroller to: allocate a set of subframes in one periodic group ofsubframes to a group of user equipments (“UEs”), allocate a subset ofthe set of subframes for a UE in the group of UEs, wherein the UE isallowed to transmit information in the subset of the set of subframes,but not in remaining subframes of the allocated set of subframes, signalthe allocated set of subframes and the allocated subset of the set ofsubframes, transmit one or more parameters, including a group identifierparameter, wherein the one or more parameters are related to a group ofHybrid Automatic Repeat reQuest (“HARQ”) processes for a direct mobilecommunication (“DMC”) link, and wherein the one or more parameters areconfigured to enable the group of UEs to manage the group of HARQprocesses for the DMC link, and perform HARQ processes for cellular UEtransmission independently from HARQ processes of the group of HARQprocesses for the DMC link, wherein the group of HARQ processes for theDMC link are allocated by the communications controller.
 22. A userequipment (“UE”), comprising: a transceiver; and a processor unitcoupled to the transceiver, the processor unit, in conjunction with thetransceiver, configured to cause the UE to: receive from acommunications controller an allocation of a set of subframes for agroup of UEs for a direct mobile communication (“DMC”) link, receivefrom the communications controller an allocation of a subset of the setof subframes for the UE, wherein the allocated subset of the set ofsubframes is a subset of the allocated set of subframes, and wherein theUE is allowed to transmit information in the allocated subset of the setof subframes, but not in remaining subframes of the allocated set ofsubframes, receive, from the communications controller, one or moreparameters related to a group of Hybrid Automatic Repeat reQuest(“HARQ”) processes of the DMC link, maintain a group of HARQ processesof a cellular UE transmission and at least one HARQ process from thegroup of HARQ processes of the DMC link, wherein the at least one HARQprocess is performed independently from the group of HARQ processes ofthe cellular UE transmission, and map the at least one HARQ process fromthe group of HARQ processes of the DMC link based on the allocated setof subframes and the received one or more parameters, including a groupidentifier parameter.